In both centralized and distributed wireless networks, beacons are widely used to convey important control information between wireless devices. For example, when a “new” wireless device is just turned on, or just moved into an area where one or more other wireless devices (e.g., a wireless access point) are already operating, the beacon includes important information that allows the “new” wireless device to establish communications with the other existing wireless device(s). Such information may include timing information for synchronizing communications between the wireless devices, operating channels or frequencies, time slot assignments for data transmission, etc.
In the past, beacons typically have been broadcast so that any wireless device in the transmission range of the beaconing device can receive the beacon.
However, in next-generation wireless networks, wireless devices of different levels of complexity and cost are expected to share the same spectrum resources in a given vicinity. There are expected to be some “advanced” wireless devices (perhaps used in applications or apparatuses where cost is less of an issue) that have more advanced capabilities sharing spectrum with other “simple” wireless devices (perhaps used in applications or apparatuses where cost is more of an issue) that have reduced capabilities. In particular, the advanced wireless devices are expected to be able to communicate using a complicated but robust communication scheme, while the simple wireless devices communicate using a simpler, less robust communication scheme. One example of this situation is illustrated by Wireless USB devices which communicate in accordance with the WiMedia common radio platform.
However, when these advanced wireless devices try to communicate in a given frequency band in a given geographical region, and the simple wireless devices try to communicate in the same or an overlapping frequency band in the same or overlapping geographical region, potential problems exits.
FIG. 1 illustrates an example arrangement 100 of wireless devices that illustrates this situation.
Arrangement 100 includes two simple wireless devices (SD) 110 operating in an overlapping frequency band in a same region as one advanced wireless device (AD) 120. In arrangement 100 illustrated in FIG. 1, advanced wireless device 120 transmits control frames or beacons 125 using a relatively complicated but more robust scheme. Meanwhile, simple wireless devices 110 transmit control frames or beacons 115 using a relatively simple but less robust scheme.
However, there is a co-existence problem between the simple wireless devices 110 and advanced wireless device 120. In particular, in arrangement 100, simple wireless devices 110 cannot receive or decode beacons 125 of advanced wireless device 120 due to the reduced capability of simple wireless devices 110. Therefore, simple wireless devices 110s may not be able to synchronize with advanced wireless device 120 so that their transmissions do not interfere with each other.
Accordingly, it would be desirable to provide a method of synchronizing wireless devices in a wireless network where one or more wireless devices operate with one type of beacon, and one or more other wireless devices operate with another type of beacon. It would further be desirable to provide wireless devices capable of performing such a synchronization method with devices using a different type of beacon.
In one aspect of the invention, a method of synchronization is provided for a system that is adapted to include at least two different types of wireless devices including Type-A wireless devices and Type-B wireless devices, wherein Type-B wireless devices are adapted to transmit Type-A beacons having a first format and Type-B beacons having a second format different from the first format and to receive only the Type-B beacons having the second format, and wherein Type-A wireless devices are adapted to transmit and receive only the Type-A beacons having the first format. The method comprises the following steps. When the first Type-A wireless device receives at least one Type-A beacon from one or more Type-B wireless devices, then the first Type-A wireless device is synchronized to the Type-B wireless device having the slowest clock, and transmits Type-A beacons that indicate that the first Type-A wireless device is operating as a forced synchronization device. When the first Type-A wireless device does not receive any Type-A beacons from any Type-B wireless devices, and receives a Type-A beacon from a second Type-A wireless device which Type-A beacon indicates that the second Type-A wireless device is operating as a forced synchronization device, then the first Type-A wireless device is synchronized to the second Type-A wireless device from now on and transmits Type-A beacons that indicate that the first Type-A wireless device is also operating as a forced synchronization device. When the first Type-A wireless device does not receive any Type-A beacons from any Type-B wireless devices, and receives a Type-A beacon from a second Type-A wireless device which Type-A beacon indicates that the second Type-A wireless device is not operating as a forced synchronization device, then the Type-A wireless device with a faster clock is synchronized to the Type-A wireless device with a slower clock and transmits Type-A beacons that indicate that the first Type-A wireless device is not operating as a forced synchronization device. When the first Type-A wireless device is operating as a forced synchronization device synchronized to a first Type-B wireless device, and the first Type-A wireless device receives a Type-A beacon from a second, alien Type-A wireless device which Type-A beacon indicates that the second Type-A wireless device is operating as a forced synchronization device that is synchronized to a second Type-B wireless device, then at least one of the Type-A wireless devices switches to another channel.
In another aspect of the invention, a method of synchronizing a first wireless device in a wireless network comprises: receiving at least one beacon of a first type; synchronizing the first wireless device based on a timing of the at least one beacon of the first type; and whenever the first wireless device synchronizes itself to a timing of a second wireless device that is unable to receive beacons of the first type, then marking the first wireless device as a forced synchronization device and transmitting beacons of the first type from the first wireless device that indicate that the first wireless device is operating as a forced synchronization device.
In still another aspect of the invention, a wireless device adapted to operate in a wireless network comprises: a transmitter; a receiver; and a clock. The receiver is adapted to receive at least one beacon of a first type and the clock is adapted to be synchronized based on timing of the at least one beacon of the first type. Whenever the clock is synchronized to a second wireless device in the wireless network that is unable to receive beacons of the first type, then the wireless device marks itself as a forced synchronization device, and the transmitter transmits beacons of the first type that indicate that the first wireless device is operating as a forced synchronization device.